A motor-driven pneumatic percussion mechanism in a hand-held machine tool is intended to provide a chiseling effect as soon as possible after being placed on a workpiece. When the tool is lifted from the workpiece the blows from the percussion mechanism are dissipated, and the energy of the blows is transmitted into damping elements and a housing of the hand-held machine tool. The resulting increased stress on the hand-held machine tool and the user should be avoided by switching off the pneumatic percussion mechanism.
DE 198 28 426 A1 describes a system for switching off a pneumatic percussion mechanism after a blank blow. Multiple ventilation holes are provided in a cup-shaped exciter cylinder, parallel to the impact axis. The ventilation openings are closed or opened to the inside by a free piston, and are closed or opened to the outside by a guide tube, depending on the relative position of the free piston and the guide tube. Slots which are longer than the free piston are provided in the exciter cylinder, parallel to the ventilation openings, to compensate for air losses in the pneumatic chamber.